replacing a starter, this is one where i rewound the pull-in coil to get more force as sometimes the starter would not work.
shown is the 500 turn rewind i did to run some tests on the plunger for permeability and the pull-in coil for inductance,
parts is parts>

 

planetary gear setup,

 

the brushes were getting down there after 20 years of operation,

this is why people hammer on there starters to get them to work, it can jog a stuck brush back against the commutator.

 

contacts are pretty well knackerd, glad to be replacing the starter at this time,

 

needle bearings support one end of the shaft,

 

magnets are held in place by a pressed in stainless gizmo, and there are nubs stamped into the case to limit horizontal travel,

 

the pull-in coil that i rewound for more pull-in sits over the hold coil which uses thicker wire for more current and thus more ampere-turns to hold the contacts closed until the key is released. as soon as the pull-in coil closes the contacts, it is out of circuit and the main coil takes over, feeding current to the stator via the contacts. there are about 100 turns on the pull=in coil as well as the hold coil. #24 AWG enameled copper wire was used to rewind the pull-in coil.

Another reason people hammer on their starters besides to free the brushes is to free the plunger which can become stuck inside the stainless sleeve due to the tight tolerances. The less air gap between the plunger and the coil, the more force,

 

rewound the coil former with 500 turns of magnet wire, this is to get a more accurate number for inductance as well as making a pull test easier to perform as the more turns, the less current i need from the power supply. The hold coil has a DCR of about 0.3 ohms so it will drag about 42 amps while the starter is cranking. I would need a car battery to supply that much current and i do not want to do that.

we hot glued a 1 lb roll of solder to the plunger to see how much voltage and current we needed to lift it off the ground. 48 volts at 60 Hz and a current draw of about 3 amps was needed.
So with 500 turns that translates to about 1500 ampere-turns and an inductance of 40 milli-Henrys at 60 Hz. The DCR of the pull-in wind was about 1.3 ohms which means that the current draw would have been about 37 amps but with the plunger adding to the inductance of the coil, current was limited to 3 amps due to the Inductive Reactance of the coil/core.
The DCR of the coil is taken at a right angle to the Reactance so solving for the triangle for the Hypotenuse yields an impedance of 15.05 ohms.